In Optics Letters, Vol. 4 No. 2 February 1979, pp. 58-59, R. Normandin (the present inventor) et al, reported the non-linear mixing of oppositely propagating guided waves. The resultant field was coupled to radiation modes and propagated in a direction perpendicular to the waveguide surface, in the case of equal frequency fundamentals. In subsequent articles, its application to picosecond signal processing, the creation of all optical transient digitizers and spectrometers demonstrated the potential usefulness of this work. (See Appl. Phys. Lett. 36 (4), Feb. 15, 1980, pp. 253-255 by R. Normandin et al; 40 (9), 1982, pp. 759-761 by R. Normandin et al, and "Integrated Optical Circuits and Components" edited by L. D. Hutcheson, Dekker Inc., New York, U.S.A., Chapter 9, by G. I. Stegeman et al.) The overlap of the two oppositely propagating fields will give rise to a nonlinear polarization source at the sum frequency. In bulk media such a process is nonradiative due to the simultaneous requirement of energy and momentum conservation in all directions. This is not the case in a waveguide geometry.
Unfortunately, since the waves do not grow with distance, (no phase matching) the resultant fields are much weaker than that obtained in a traditional second harmonic generation device. Therefore, this nonlinear interaction has remained largely a laboratory curiosity. However in U.S. Pat. No. 5,051,617, entitled Multilayer Semiconductor Waveguide Device for Sum Frequency Generation From Contra-Propagating Beams, the present inventor has increased this interaction by factors of 10.sup.7 to obtain efficient conversion in the visible region. Thus, with the invention disclosed in U.S. Pat. No. 5,051,617, ultra fast subpicosecond samplers and monolithic high resolution spectrometers are possible in the context of fiber optic communication systems and optoelectronic integrated circuitry. Although the invention disclosed in U.S. Pat. No. 5,051,617 adequately performs it's intended function, there is a requirement for a device which will allow a sum frequency output wave to be directed in any one of a plurality positions in a plane in space in a controlled manner.
When two guided fundamental wavelengths are identical, oppositely propagating and traveling in the same collinear and one dimensional path, the radiated harmonic signal is observed in a direction perpendicular to the surface of the waveguide. When the two oppositely propagating optical signals are of differing wavelength, wave vector addition rules coupled with energy conservation rules dictate the angle of emission as well as the sum harmonic wavelength.
U.S. Pat. No. 5,111,466 in the name of the Normandin (the applicant) et al. issued May 5, 1992 and entitled "Optical Multilayer Structures for Harmonic Laser Emission", discloses that two counter-propagating lights which are contained in an optical waveguide along a single dimension can interact and form a second harmonic optical signal which is emitted from the optical waveguide in a direction different from the single dimension, and thus can be detected outside the waveguide. The disclosed waveguide is formed of layers of semiconductor material having different indices of refraction. The thicknesses of the layers and their periodicity determine the bandwidth and relative wavelengths of the two input signals determine the angles of emission of the harmonic signal. In FIG. 9 of the drawings, it is shown that if the two counter-propagating optical signals are mixed in a non-linear waveguide, and one of those signals has a fixed frequency, the angle of emission of the output signal will change as the frequency of the other optical signal varies. If plural multiplexed optical signals having different frequencies were each selectively combined with a counter-propagating reference signal having a fixed frequency in the optical waveguide, the output signal of each combined pair would have a differing angle of emission. Normandin et al. disclose that with several fixed detectors in the far field, multichannel detection can be reconfigured at will by switching the reference beams and adjusting them in frequency to direct each channel on the desired detector position. Although directing each channel to a desired detector position in this manner may be useful, it would be more advantageous to have additional control allowing any input channel to be directed to any one of a plurality of far field detectors. For instance, this would be useful in the field of telecommunications where one channel could be connected to any of a plurality of other channels.
This invention is thus relevant to spatially addressable coherent detectors, optical data storage and retrieval systems, fiber optical communication systems and optoelectronic communication systems, to name a few.